Merchiston Castle was probably built around 1454 by Alexander Napier, the second Laird of Merchiston, and is most famous for being the birthplace in 1550 of John Napier, the discoverer of logarithms, and the 8th Laird of Merchiston.
The tower passed in and out of Napier hands over five centuries, and in 1833 William Napier, the 9th Lord Napier, let the castle to Charles Chalmers, who established Merchiston Castle School in the building.
The school moved to Colinton in 1930, and by 1935 the castle had passed to the Edinburgh Corporation. It remained unoccupied and deteriorating until 1956 when it was decided that the castle would be the centrepiece in the development of the new Napier Technical College (now Napier University).
Originally a five-storey L-plan tower and surrounded by a barmkin wall, it had a drawbridge at second floor level some 4.3m above the ground (discovered during the restoration work in 1958).
The castle is built on a rocky outcrop – hard to envisage with all the concrete surrounding it, but still visible at the base of the tower in places.
In the late 17th century the present roof and buildings above the parapet walk were added, possibly by the Lowis family.
A number of outbuildings were added while the castle was being used as a school, although these were removed during renovation work. One extension remains to the north, now pierced by a corridor connecting the castle to other campus buildings.
Within Merchiston Castle is an ornate painted ceiling dating to 1581, which was removed from Prestongrange House.